The present invention relates to automatic control of plastic flow through injection nozzles in a molding machine. More particularly the invention relates to proportional control of plastic flow via proportional control of the actuator mechanism for a valve for a nozzle particularly where two or more nozzles are mounted on a hotrunner for injection into one or more mold cavities. The proportional control is achieved via the use of one or more sensors which senses a selected condition of the plastic flow through a manifold, nozzle or into a mold and the use of the recorded condition in conjunction with a selected nozzle design, hotrunner/manifold design, actuator design, actuator drive mechanism and/or flow control mechanism. Proportional control of melt flow typically refers to control of the rate of melt flow according to an algorithm utilizing a value defined by a sensed condition as a variable.
In accordance with the invention there is provided an apparatus and method for proportionally controlling the rate of melt flow through a melt flow path in an injection molding machine, in particular controlling the melt flow through two nozzles.
More particularly, there is provided in an injection molding machine having first and second nozzles for delivering melt material from a common manifold to one or more mold cavities, an apparatus for controlling delivery of the melt material from the nozzles to the one or more mold cavities, each nozzle having an exit aperture communicating with a gate of a cavity of a mold and being associated with an actuator interconnected to a melt flow controller, the apparatus comprising:
a sensor for sensing a selected condition of the melt material through at least one of the nozzles; and,
an actuator controller interconnected to each actuator, each actuator controller comprising a computer interconnected to a sensor for receiving a signal representative of the selected condition sensed by the sensor, the computer including an algorithm utilizing a value corresponding to a signal received from the sensor as a variable for controlling operation of an actuator for the at least one nozzle.
At least one of the nozzles most preferably has a seal surface disposed on a tip end of the nozzle which is engaged and in compressed contact with a complementary surface surrounding the gate of a cavity of a mold, the engaged surfaces forming a seal against leakage of the melt material around the nozzle and maintaining the pressure of the melt against loss of pressure due to leakage. The at least one nozzle is typically expandable upon heating to a predetermined operating temperature, the nozzle being mounted relative to the surface surrounding the gate such that the seal surface disposed on the tip end of the nozzle is moved into compressed contact with the complementary surface surrounding the gate upon heating of the nozzle to the predetermined operating temperature. The complementary mating surfaces of the nozzle and the gate area of the mold are typically radially disposed relative to the axis of the exit aperture of the nozzle, although the mating surfaces may also be disposed longitudinally or axially.
The tip end of the nozzle may comprise a single unitary piece or, in another embodiment, an outer unitary piece formed of a first material and an inner unitary piece formed of a second material, the first material being substantially less heat conductive than the second material. The complementary mating surfaces of the nozzle and the gate area of the mold are typically radially disposed relative to the axis of the exit aperture of the nozzle, although the mating surfaces may also be disposed longitudinally or axially.
At least one of the nozzles may have a tip end having a central portion having a central bore in alignment with a gate and an outer circumferential flange portion surrounding the gate and the central portion of the tip end of the at least one nozzle.
The melt flow controller of the apparatus typically comprises a pin which is controllably slidable via interconnection to an actuator along a reciprocal path of movement within the bore of a nozzle, or the controller typically comprises a rotary valve having a rotatable flow channel connecting an input flow channel to the exit aperture of at least one of the nozzles, the rotatable channel being interconnected to the actuator and controllably rotatable via the actuator to selectively vary the rate of flow of plastic melt through the rotatable flow channel to the exit aperture according to the degree of rotation of the rotary valve. The rotary valve typically comprises a cylinder rotatably mounted within a housing the cylinder having a bore rotatably communicable with a pair of bores in the housing.
One or more actuators may comprise a piston mounted within a fluid sealed housing, the piston having a stem extending outside the fluid sealed housing, the valve pin having a head wherein the stem is readily detachably interconnected to the head of the valve pin outside the fluid sealed housing.
One or more actuators may comprise an electrically driven motor, the motor being mechanically interconnected to either a valve pin disposed in a bore of one of the nozzles such that the valve pin is reciprocally drivable within the bore of the nozzle by the motor, or a rotary valve for rotatable drive of a rotatable component having a fluid flow bore, the motor being electrically interconnected to the algorithm, the algorithm controlling the drive of the motor.
Each actuator for each of the first and second nozzles may be fluid driven wherein each actuator is commonly supplied with an actuator drive fluid flowing through a manifold which commonly delivers fluid to each of the nozzles.
The actuator controller for a fluid driven actuator typically comprises a solenoid having a piston controllably movable between selected positions for selectively delivering a pressurized actuator drive fluid to one or the other of at least two chambers of the actuator
The actuator controller for a fluid driven actuator may include a drive fluid valve which receives pressurized drive fluid from a source, the drive fluid valve having one or more fluid ports sealably communicating with one or more complementary fluid drive chambers disposed within the fluid driven actuator, the drive fluid valve being controllably driven to selectively distribute received pressurized fluid through the one or more fluid ports to the one or more complementary fluid drive chambers of the actuator. The drive fluid valve typically comprises a sealed housing and a plunger movable within the sealed housing to positions along a path wherein the one or more fluid ports are open to communication, partially open to communication, or closed from communication with the one or complementary fluid drive chambers by the plunger, the plunger being controllably movable to any position along the path between the open and closed positions such that flow of the drive fluid to a drive fluid chamber is controllably variable to a selected rate. The plunger typically comprises a slidably movable rod having interference projections which are selectively slidable by movement of the rod over the fluid ports to open, partially open to any desired degree, or close the fluid ports.
In another embodiment, at least one gate of a mold may be an edge gate extending radially outward through a mold cavity plate, at least one of the nozzles having a bore having a first portion having an inlet for the plastic melt which is not in alignment with the edge gate and a second portion extending radially outward from the first portion terminating in the exit aperture being in alignment with the edge gate. In such an embodiment the nozzle may have an exit end comprising a center nozzle member and a circumferential nozzle member surrounding the center nozzle member, the exit aperture extending through the center nozzle member in alignment with one of the gates, the circumferential nozzle member surrounding the one gate, wherein a groove is formed between the circumferential nozzle member and the center portion.
The apparatus typically includes a plurality of enclosed heat conductive tubes containing a fluid which vaporizes and condenses within each tube and a wick disposed within and along the length of each tube, at least one of the manifold and one of the nozzles having the tubes embedded within the manifold or the nozzle making heat conductive contact with the manifold or the nozzle.
The apparatus may include a melt flow reservoir sealably communicating with and disposed between a common feed channel of the manifold and an exit aperture of a nozzle, the reservoir having a defined volume sealably fillable and closed off from communication with the common feed channel, the reservoir including an injection mechanism operable on melt material residing in the reservoir to force the melt material through the exit aperture of the nozzle under pressure. In such an embodiment, the melt flow controller preferably comprises a valve disposed in the melt flow between the reservoir and the exit aperture of the nozzle. The melt flow controller may also alternatively comprise the injection mechanism.
The sensor typically comprises a pressure transducer interconnected to at least one of the bore of a nozzle or a mold cavity for detecting the pressure of the melt material. The sensor may comprise a mechanism selected from the group consisting of a pressure transducer, a load cell, a valve pin position sensor, a temperature sensor and a barrel screw position sensor.
In a typical embodiment, at least one of the nozzles has a bore, a valve pin as the flow controller and a surface for forming a gap with a surface of the bore away from the gate, wherein the size of the gap is increased when the valve pin is retracted away from the gate and
decreased when the valve pin is displaced toward the gate. Alternatively the valve pin and the bore may be configured such that valve pin has a surface for forming a gap with a surface of the bore away from the gate, wherein the size of the gap is decreased when the valve pin is retracted away from the gate and increased when the valve pin is displaced toward the gate. In such embodiments the apparatus typically includes a plug mounted in a recess of the manifold opposite a side of the manifold where the at least one nozzle is coupled, the plug having a bore through which a stem of the valve pin of the nozzle passes, the valve pin having a head which has the surface which forms the gap with the complementary surface of the bore, the bore of the plug through which the stem passes having a smaller diameter than the valve pin head at the valve pin head""s largest cross-sectional point and the recess of the manifold having a larger diameter than the diameter of the valve pin head at the valve pin head""s largest point, so that the valve pin can be removed from the manifold from a side of the manifold in which the recess is formed when the plug is removed from the manifold.
The apparatus most preferably includes a second sensor for sensing a second selected condition of the melt material through the second nozzle, the computer being interconnected to the second sensor for receiving a signal representative of the selected condition sensed by the second sensor, the computer including an algorithm utilizing a value corresponding to a signal received from the second sensor as a variable for controlling operation of an actuator for the second nozzle.